1. FIELD OF INVENTION
The present invention relates to the manufacture of hollow articles from extruded tubes by blow molding. More particularly, the invention relates to the manufacture of containers having compartments that are partitioned off from each other and have separate pouring openings, yet are interconnected in back-to-back fashion and, especially, apparatus for production of such containers.
2. DESCRIPTION OF RELATED ART
Containers which combine two individual containers into a single dual-compartment container are known. Such two-compartment containers are convenient, for example, for the storage of two different fluids, such as gasoline and lubricating oil for the preparation of fuel mixtures for two-stroke engines. It is also known to be able to produce such dual-compartment containers, wherein the compartments are separated and each compartment has its own pouring opening, by a process known as extrusion blow molding.
An example of an apparatus for the blowing of a two-compartment container can be found in U.S. Pat. No. 3,724,987. In accordance with this patent, an extruder extrudes a single tube of hot thermoplastic material in a vertical direction and two blow mold halves clamp onto the extruded tube. In each blow mold half, a mold cavity is formed that has a separating wall which is designed to vertically pinch the extruded tube so as to form a partition between the two compartments. A respective blow pin is displaced in a parting plane of the mold so as to enter into the tube at each of opposite sides of the pinched partition. Air at approximately 10 atmospheres pressure is directed by blow pin into each compartment for expanding of the tube into engagement with the walls of the mold cavity to form the container. Cooling of the blown container is achieved by the circulation of cold water through the mold walls, including separating wall. The blow pins, which are mounted on separate carriers for carrying out similar, but opposite, compound movements, also serve in conjunction with a threaded mold wall surface for forming a threaded spout-type pour opening on the container for each compartment.
However, such apparatus has deficiencies in several respects. Firstly, because the blow pins are separately mounted and must carry out composite movements in opposite directions, the cost and complexity of such an apparatus is greatly increased (making it, in a number of cases, infeasible to use with existing extrusion blow molding equipment). Also, it is virtually impossible to utilize multicavity molds, thereby precluding the possibility of simultaneously producing a plurality of containers at a single blowing station, thereby imposing drastic limitations on production capacity. Furthermore, even though the blowing operation for a given size container is shorter for a compartmented container than an uncompartmented one, because the thickest portion of the container remains to be the spout area which is not thinned due to the stretching occurring during inflation of the parison (and is actually thickened in the case of a threaded neck-type pouring opening), and because it is not subjected to the cooling effects of the air blown into the parison for inflation purposes, in order to avoid distortion of the pouring opening, the molds must remain closed for substantially the same length of time as would be the case for a single compartment container of comparable size to achieve sufficient cooling of the pouring opening.
Therefore, relative to such apparatus for producing dual compartment containers, the need exists for a means to increase production capacity, both in terms of the number of articles that can be produced at a single blowing station and in terms of the cycle time required before the mold can be opened for discharge of the blown container.
An extrusion blow molding apparatus is known from U.S. Pat. No. 3,075,239, wherein the mold is provided with a plurality of cavities whereby a like number of containers can be simultaneously blown via blow pins which are mounted to a common support bar for reciprocation toward and away from the mold. For cooling the neck of the container which defines the pour opening thereof, the blow pins are cooled, in the blowing position thereof, by having them extend through apertures formed in a stripper bar-carried, water-cooled tank. However, since there is no direct cooling of the tip portion of the blow pins and the water tank surrounds only an axially central portion of the blow pins, the tip portion, which requires the greatest cooling, is the least effectively cooled portion. Furthermore, such an indirect cooling technique is highly inefficient in that the heat must be conducted along the length of the blow pins to the area of the cooling tank. Additionally, because of the size of the water chamber of the cooling tank that must be disposed between the pins to produce a sufficient cooling effect, limitations are placed upon the minimum radial spacing between blow pins which, although adequate for the purpose of producing separate single compartment containers in a single mold, places undesirable limitations upon the placement of the pouring openings of the separate compartments of a dual compartment container. In some cases, this may prevent the pouring openings from being placed sufficiently close together to enable production of smaller size containers.
Therefore, relative to such a cooled blow pin arrangement, the need exists for a more effective means for cooling the tip of the blow pins and for a means to enable such cooling to be achieved without imposing undesirable limitations upon the minimum spacing at which one blow pin can be positioned relative to another.
In the injection blow molding of containers (as opposed to the extrusion blow molding thereof), parisons are formed in an injection mold about a core pin. The injection molded parison is then transferred on the core pins from the injection mold to a blow mold having a larger cavity. At the blow mold, the core pin serves as a blow pin and for insuring that the parison is at the proper temperature for blowing within the blow mold, it is conventional for a liquid heat transfer medium to be circulated through the length of the core/blow pin in order to heat and/or cool the parison, as appropriate. However, in such injection blow molding apparatus, the tip of the core/blow pin having the blowing air nozzle is positioned well within the cavity of the blow mold in the portion at which the bottom half of the container is to be formed. Also, the container neck forming the pouring opening is formed against an intermediate or base portion of the core, at the edge of the mold through which it is inserted. Additionally, the circulation of the liquid heat transfer medium through the core pin is designed to substantially uniformly maintain the temperature of the parison and no attempt is made to preferentially cool the portion at which the pouring opening is formed. On the other hand, the arrangements by which heat transfer mediums are delivered to and circulated through the core/blow pins imposes no undesirable spacing limitations and, in fact, it is commonplace for a plurality of such core/blow pins to be mounted upon a single support, and it is known for such a common support to function as a manifold for the delivery and return flow of the heat transfer medium and for supplying the blowing air. Examples of such injection blow molding apparatus can be found, for example, in U.S. Pat. Nos. 3,690,802; 3,998,577; 4,285,657; 4,363,619; and 4,473,515, to name a few.
Applicants have found that it would be desirable if the fluid heat transfer medium circulation techniques used in the injection blow molding art could be adapted to the needs that they have found to exist in the extrusion blow molding field, particularly in connection with the production of dual-compartment containers.